Neutralizing condenser



Sept. 17, 1929. H ELLIOTT 1,728,201

NEUTRALI Z LNG CONDENSER Filed May 24, 1926 m l+ f z/ H HI5 ATTORNEY Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE HAROLD I. ELLIOTT, OF PALO ALTO, CALIFORNIA, ASSIGNOR, BY DIRECT AND MESNE ASSIGNMENTS, TO VICTOR TALKING MACHINE COMPANY, OI CAMDEN, NEW JER- SET, A CORPORATION OF NEW JERSEY NEUTRALIZING CONDENSER Applicationflled May 24, 1926. Serial No. 111,295.

This invention relates to electronic emis- .ion devices, such as audions, and more particularly to a scheme whereby the capacity between certain of the electrodes in the 5 audions or vacuum tubes may be neutralized. One such scheme is described in a Patent, N 0. 1,334,118, issued March ,16, 1920, in the name of C. W. Rice. In that system, as well as in several others hereinafter referred to, It is necessary to employ a neutralizing condenser for overcoming the tendency of the audionto roduce undesired oscillations. It is one of t eobjects of my invention to provide a neutralizing capacity effect in an .5 extremely simple and convenient manner.

Thermionic tubes, or audions are now new ally provided with prongs or projections by the aid of which connections may be made externally of the tube, to the various elec- 0 trodes within the tube. It is another object of my invention to utilize one of these prongs as an electrode or late of a condenser, which can be used or neutralizing purposes.

It is still another object of my invention to provide a simple and inexpensive neutralizing condenser that, can furthermore be readily adjusted to take care of the varying conditions met with.

I My invention possesses many. other advantages, and has other objects which may be made more easily apparent from a consideration of one embodiment of my invention. For this purpose I have shown a form in the drawings accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the append-o ed claims.

Referring to the drawings Figure 1 is a View, partly sectional, of an audion and its mounting, together with the elements that provide a neutralizing capacity effect; l

Fig. 2 is a wiring diagram showing the application of my invention to a neutralizing radio frequency amplifier system; and

Fig. 3 is a perspective view of some of the parts forming the neutralizing capacity.

Referring first to Fig. 2, I show a conventional absorbing circuit, consisting ,of elevated conductors 11, a loading inductance 12, and a ground connection 13. An audion 14, having a filament. 15, adapted to be heated by the passage of an electric current to cause it to emit electrons, is arranged to be affected'by the weak impulses received in the circuit 11-12-13. As is usual, the audion 14 has a cold electrode or anode 16, in the form of a plate, spaced from filament 15 and kept at a potential positive with respect to the filament, for attracting the electrons. For this purpose, a battery 17 is shown as included in an external circuit connecting these two electrodes.

It is now well' understood that by varying the potential of a point in the space between the filament 15 and late 16, magnified variations in electron ow forming the space current between these electrodes are produced. For controlling the potential of such a point in the space, a control electrode or grid 18 is provided. In order to vary the relative potentials of the grid- 18 and filament 15 in accordance with the radio frequency signals received by absorbing circuit 11--1'2'-13, the upper portion of acoil 19 coupled-to loading coil 12, is included in an external circuit connecting the electrodes 15 and 18. In this manner, potential difl'erences varying in accordance with the signallng impulses, are impressed between these two electrodes, and cause corresponding current variations in the external circuit connecting plate 16 and filament 15. This circuit includes, besides battery 17, a translating device such as a transformer 20, for transferring the amplified signaling impulse to a succeeding stage, or to a detecting de vice, in a well-understood manner. A bypass condenser 21 can be provided to shunt battery 17 and to carry the high frequency impulses; and a tuning condenser 22 can also be used to provide a resonant circuit with coil 19. I

As thus far described, the system differs in no material way from other radio freqency amplifier systems. A parasitic capacity coupling exists between grid 18 and plate 16, which may give rise to instability. This coupling can e considered as producing an E. M. F. across these electrodes. In

order to neutralize this E. M. F., use is made of a neutralizing circuit, extending from plate 16 to filament 15, and including a capacity 23, and the lower portion of coil 19. When the upper and lower portions of coil 19 are exactly equivalent, then capacity 23 should be adjusted to be equal in value to the'capacity betweengrid 18 and plate 16, in order to secure complete neutralization. All this is explained in the Rice patent referred to, as well as the theory upon which the neutralization rests.

The present invention is concerned with the manner in which variable capacity 23 is secured." Referring to Fig. 1, the tube 14 is shown as mounted in a socket 24, gripped in a soft rubber ring 25. This ring can be held to a support 26 by the aid of a flanged metal ring 27. The prong or bar 28 which serves as the connection to the plate 16, projects through socket 24, and is utilized as one electrode of the capacity 23. The other electrode is shown as a split tube 29 (Fig. 3) which has an insulation tube 30, therein,

such as of varnished cambric or the like,

This tube 29 can be slipped frictionally over the post or prong 28, and by moving it axially, as by the aid of the knob, the capacity between it and prong 28 can be set to the desired value.

I claim:

1. The combination, with an audion tube having a plurality of electrodes, and a post forming an external connection means for one of the electrodes, of a metallic sleeve disposed over said post but spaced therefrom and forming a condenser therewith.

2. The combination, with an audion tube having a plurality of electrodes and a post forming an external terminal for one of the electrodes, of a metallic split sleeve and an insulation tube within the sleeve, frictionally engaging said post and forming a condenser therewith.

3. The combination, with an audion tube having a control electrode and a post forming an external terminal for the electrode, of a metallic split sleeve and an insulation tube within the sleeve frictionally engaging said post and forming a condenser therewith.

In testimony whereof I have hereunto set my hand.

, HAROLD F. ELLIOTT. 

